Nonvolatile memory devices are widely installed in mobile devices such as mobile phones and digital cameras, and are finding rapidly increasing use. Recent years have seen more opportunities to handle audio data and image data, creating a growing demand for nonvolatile memory devices that have larger capacity and operate faster than ever. There is also a pressing need for lower power consumption of nonvolatile memory devices for use in mobile devices.
A flash memory is a predominant nonvolatile memory device today. In the flash memory, data is written by controlling a charge accumulated on a floating gate. Since the flash memory has a structure of accumulating a charge on a floating gate in a high electric field, its miniaturization is limited, and microfabrication necessary to attain larger capacity is difficult. Besides, to rewrite the flash memory, a predetermined block needs to be erased at a time. Due to such a property, rewriting the flash memory requires a very long time. This poses random access and speed-up limitations.
As a next-generation nonvolatile memory device for solving these problems, there is a nonvolatile memory device using a variable resistance element in which information is written by a change in electrical resistance. As such a nonvolatile semiconductor device (also referred to as “nonvolatile memory”) using a variable resistance element, an MRAM (Magnetic RAM), a PCRAM (Phase-Change RAM), a ReRAM (Resistive RAM), and the like are currently proposed (see, for example, Patent Literatures (PTLs) 1 to 3).